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Introduction Only about 30% of pediatric patients with Graves’ hyperthyroidism achieve remission with medical therapy, and therefore radioactive iodine (RAI) therapy is often used as a definitive treatment. Although the goal of RAI is permanent hypothyroidism, this is not consistently achieved. We conducted a chart review to determine the factors associated with the success of RAI. We also tried to determine optimal follow-up post RAI and if there was an optimal L-thyroxine dose that would normalize the hypothyroid state quickly. Methods This is a retrospective chart review of Graves’ patients who underwent RAI between 2008 and 2017. We included age, sex, time from diagnosis, thyroid gland size, total dose of I-131 and dose in μCi/g of thyroid tissue. Patients were grouped based on outcome and analyzed using univariate and multivariate logistic regression. Follow-up thyroid levels post RAI and after starting l-thyroxine were analyzed. Results There were 78 ablations including six repeat ablations. Seventy-three percent became hypothyroid, 23% remained overtly or subclinically hyperthyroid, and 4% were euthyroid. Smaller thyroid size (36.5 vs. 47.4 g; p = 0.037) and higher dose of I-131 (242 vs. 212 μCi/g thyroid tissue; p = 0.013) were associated with a higher likelihood of hypothyroidism. Most patients remained hyperthyroid at 1 month post RAI, but by 3 months the majority became hypothyroid. There was no clear L-thyroxine dose that normalized hypothyroidism quickly. Conclusions An I-131 dose close to 250 μCi/g of thyroid tissue has a higher likelihood of achieving hypothyroidism. Testing at 2–3 months after RAI is most helpful to confirm response to RAI.

Hyperthyroidism is much less common in children To compare the mean MMI dose needed to normalize free T4 in younger (Based on chart review (2004–2012), patients were divided into groups based on age at diagnosis: 12 years (n=40). Follow-up visits were reviewed until free T4 normalized.The mean dose of MMI (mg/kg/day) needed to normalize free T4 was 0.71 (±0.29) in the Hyperthyroid children diagnosed before age 7 required higher initial doses of MMI and took a longer time to become euthyroid than older patients. Clinicians should consider starting with higher weight-based MMI doses when treating younger patients to more rapidly normalize free T4.

AIM Although subnormal TSH between 0.1-0.4 mIU/L is fairly common and benign, suppression of TSH to < 0.1 mIU/L with normal free T4 is less common and more worrisome. We have conducted a retrospective chart review of a collection of such cases and have summarized the features and outcome on follow up. METHODS We studied 23 consecutive patients referred from 2005-07 to our pediatric endocrine clinic with TSH < 0.1 mIU/L and free T4 in the range of 0.8-2 ng/dl. We collected historical, clinical and laboratory data, and analyzed their outcome. RESULTS The natural evolutions of these subjects were separated into 4 groups. Group 1, 14 subjects, (61%) became euthyroid within a mean of 3.7 months. Group 2, 4 subjects, (17%) became hypothyroid within a mean of 2.8 months. Group 3, 2 subjects (9%) progressed to overt hyperthyroidism. Group 4, 3 subjects (13%) had persistently suppressed TSH, 8-14 months after initial testing, of which one had a multinodular goiter and had a thyroidectomy. Elevated thyroid peroxidase antibody (TPO) was seen in 54.5% of those tested. CONCLUSION Only 2/23 in our series became overtly hyperthyroid. Substantial number of subjects had a short period of transient TSH suppression that resolved spontaneously. Markers suggestive of autoimmune thyroid disease were consistently seen in group 2 and less so in others. It is prudent to observe such cases in the short term with serial follow up TSH, free T4 and T3, and to reserve further testing and treatment for those who become symptomatic or do not resolve.